The present invention relates to an apparatus for the synthesis of a diamond film utilizing an arc plasma. More particularly, the efficiency of a diamond synthesis apparatus is improved by modification of the plasma generator nozzle, shaping the plasma and thermal management of a substrate receiving the diamond film.
Synthetic diamond films are manufactured by many different processes. In one exemplary process, a carbon containing feed gas, such as methane, is decomposed to elemental carbon by injection into a plasma stream. This process is described in more detail in U.S. Pat. No. 4,767,608 to Matsumoto et al and European Patent Application Serial No. 88 302836.7 to Fujitsu Ltd., both of which are incorporated by reference herein in their entireties.
In accordance with this method, a hydrogen containing plasma source gas flows between an anode and a cathode where an electric arc generates a plasma. A hydrocarbon containing source gas is introduced into the plasma and is dissociated to carbon radicals, carbon and hydrogen. The carbon containing plasma impacts a substrate depositing the carbon radicals and carbon. Under the proper conditions, the deposition is crystalline carbon, generating a diamond film.
Among the disadvantages with the conventional process are the limited diameter of the plasma plume and the temperature gradient across the plasma plume both of which restrict the size and thickness of the deposited diamond film. The perimeter of the plasma plume cools more rapidly than the central portion. The cooler peripheral portion of the plasma plume is less effective for dissociation of the hydrocarbon containing source gas, resulting in a lower growth rate of diamond film. Additionally, the thermal gradient in the substrate causes internal strain in the deposited diamond film which can crack the film or affect the optical properties.
There exists, therefore, a need in the art for an improved apparatus for the synthesis of a diamond film utilizing arc plasma which does not suffer the limitations of the prior art.